Development and performance investigation of MgSO₄/SrCl₂ composite salt hydrate for mid-low temperature thermochemical heat storage

Salt hydrate based thermochemical heat storage (TCHS) is currently a pivotal technique used for long-term energy storage due to its reversible gas-solid reaction at middle-to-low temperature. MgSO₄ is a promising salt candidate owing to its theoretically ultrahigh energy storage density (ESD). However, its poor heat and mass transfer performance severely restricts its large-scale application. Composite salts consist of MgSO₄ and other promising salt are prepared to improve the thermochemical performance such as the adsorption kinetics. Simultaneous thermal analysis (STA) is used to screen several other potential salt candidates by comparing the ESD. SrCl₂ shows the highest ESD and is selected to mix with MgSO₄. X-ray diffraction confirms that the composite salt hydrate is successfully prepared, and the chemical composition is measured by X-ray fluorescence spectrometry. The STA results show that the mixture with an appropriate composition proportion can enhance ESD at mid-low temperatures. The mixture with 20 wt% MgSO₄ possesses the best adsorption kinetics even under the most unfavorable condition. Vapor adsorption isobars for dehydrated SrCl₂, MgSO₄, and their mixtures are measured between 30 °C and 90 °C, which is conducive to understand the chemisorption mechanism. Additionally, cyclability test results show that the aforementioned mixture has better cycle stability than do pure salts. Specifically, the heat storage capacity of the mixture stays above 75% of the original after 20 consecutive heat charging (dehydration) and discharging (hydration) cycles. All these results indicate that the composite salt has good potential for use in long-term TCHS at mid-low temperatures.